Fuel inside the fuel tank is sent to a side of the internal combustion engine through an intake pipe, and the like, disposed inside this fuel tank. A filter device is attached to the fuel intake port of such intake pipe in order to remove water from the fuel thus sent and to make it such that dust is not sent into the fuel pump. As such a filter device, there is one shown in Patent Document 1 disclosed by the present applicant.
Inside the filter device of Patent Document 1, there is a bag-like filter body having an internal space which is made to connect through to the fuel intake port inside the fuel tank. Such filter body has two layers of filter materials made of nonwoven cloth produced by melt-blown method between a filter material on the outermost layer made of woven fabric mesh and a filter material on the innermost layer made of nonwoven cloth produced by spun-bond method. Also, it is made such that the average aperture size of the nonwoven cloth produced by melt-blown method positioned on the inside becomes smaller than the average aperture size of the nonwoven cloth produced by melt-blown method positioned on the outside, whereby a filtration gradient is given to the filter body. By this, while it is made such that fine dust can be captured, the burden on the filter material made of nonwoven cloth produced by melt-blown method positioned on the inside having a small average aperture size is lessened so as to achieve a long life of the filter device.
In the filter device thus constituted, by overlaying even more filter materials made of nonwoven cloth produced by melt-blown method which makes the average aperture sizes different, (the difference of average aperture sizes of adjacent filter materials is reduced) it is possible to achieve the long life of the filter device while improving the filtering precision. However, considering the manufacturing cost, and the like, of the filter body, there is a limit to the number of filter materials overlaid. Also, because the number of filter materials at the places to be welded in order to have a bag-like shape increases as the number of filter materials overlaid becomes greater, it becomes difficult to constitute an adequate filter body by such welding.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-48721